A licensed-assisted access using Long Term Evolution (LAA-LTE, Licensed-Assisted Access Using Long Term Evolution) system may also be referred to as a Long Term Evolution unlicensed spectrum (LTE-U, Long Term Evolution Unlicensed spectrum) system. In the system, a device first detects, according to a listen-before-talk (LBT, Listen Before Talk) rule, that a channel resource in an unlicensed spectrum is idle, and then transmits data by using the channel resource in the unlicensed spectrum. The unlicensed spectrum is a common frequency resource in a wireless communications network. A licensed spectrum is a frequency resource dedicated to some operators.
Referring to FIG. 1, in the prior art, a sending device cannot learn when an unlicensed carrier can be preempted. Therefore, a time at which an unlicensed spectrum is successfully preempted may be not the start of a complete subframe. Starting from the moment at which the unlicensed carrier is preempted for data sending, an incomplete subframe A is first sent. A time of the subframe A lasts and ends at the start of a next subframe in a time on a corresponding licensed carrier. Then multiple complete subframes B are sent. Because resource waste is caused when duration in which the sending device preempts the unlicensed carrier ends at the end of a complete subframe, there is another incomplete subframe C when transmission ends. Therefore, how to set control information for the incomplete subframe A and the incomplete subframe C becomes a problem that urgently needs to be resolved.